The present invention relates to a power converter, and more particularly to a configuration of a driver circuit group for driving power transistors in a power converter.
In a matrix converter, an inverter, and the other power converters, there is frequently used power transistors (for example, IGBT (insulated gate bipolar transistor), or a MOSFET (metaloxide semiconductor field effect transistor), which can conduct a large current and block a high voltage. In the power converter, a pre-driver is generally used for driving a gate terminal of each power transistor. A signal for controlling on/off operation of the power transistor is supplied to the pre-driver from a control circuit, and the pre-driver drives the gate terminal of the power transistor in response to the control signal.
As well known by an ordinary skilled person, an electric isolation needs to be obtained between the pre-driver for driving the power transistor and the control circuit, that is, a circuit ground needs to be separated therebetween. The most typical technique for isolating the pre-driver and the control circuit from each other is to use an optocoupler. Since the optocoupler transmits a signal as an optical signal (not an electric signal), the pre-driver and the control circuit can be electrically isolated from each other with the use of the optocoupler.
However, because the optocoupler requires optical isolation between channels, it is difficult to integrate several channels of the optocoupler into an IC (integrated circuit). Accordingly, the use of the optocoupler causes the number of ICs used for the power converter to increase. For example, in a three-phase matrix converter using a pair of power transistors as a bidirectional switch, 18 power transistors are provided. In the three-phase matrix converter, optocouplers and 18 pre-driver ICs are required. As the number of ICs used for the power supply is more increased, the installation area increases more, and the costs also increases more.
A technique has also been known in which the optocoupler is replaced with a pulse transformer for the purpose of electrically isolating the pre-driver and the control circuit from each other (for example, refer to Japanese Unexamined Patent Application Publication No. 2009-219294). Also, Japanese Unexamined Patent Application Publication No. 2010-263671 discloses a technique in which the pulse transformer is replaced with a pair of coils mounted on a printed circuit board. Further, Japanese Unexamined Patent Application Publication No. Hei 5(1993)-344751 discloses a technique in which, in order to reduce the number of power supplies, the pulse transformer is used for a power transistor of an upper arm whereas no pulse transformer is used for the power transistor of a lower arm.
However, those techniques insufficiently cope with such a problem that the number of ICs used for the power converter increases.